The present invention generally relates to an amplitude detector and an equalizer.
When a video signal of R (Red), G (Green), and B (Blue) for example is transmitted through a copper monitor cable, the amplitude of the signal is detected by a destination receiver and, based on the detection result, the signal of which amplitude has been attenuated by transmission is amplified to restore the original signal.
FIG. 7 shows a constitution of a related-art amplitude detector 1 arranged in a receiver. As shown, the amplitude detector 1 has a capacitor 2, a full-wave rectifier 3, and a peak-hold circuit 4. In the amplitude detector 1, the DC component of a video signal S0 transmitted over a monitor cable is removed by the capacitor 2 and the AC component S2 of the video signal S0 shown in FIG. 8 is outputted to the full-wave rectifier 3. In the full-wave rectifier 3, the AC component S2 is full-wave rectified into a signal S3 shown in FIG. 8. In the peak-hold circuit 4, the peak voltage of the signal S3 is detected and an amplitude detect signal S1 for holding this peak voltage is outputted.
FIG. 9 shows a constitution of another related-art amplitude detector 11 arranged in a receiver.
As shown, the amplitude detector 11 has a capacitor 2, a positive peak-hold circuit 13, a negative peak-hold circuit 14, and an operational amplifier 15. In the amplitude detector 11, the DC component of a video signal S0 transmitted over a monitor cable is removed by the capacitor 2 and an AC component S2 of the video signal S0 shown in FIG. 10 is outputted to the positive peak-hold circuit 13 and the negative peak-hold circuit 14. In the positive peak-hold circuit 13, the positive peak voltage of the AC component S2 is detected and a signal S13 for holding the detected peak voltage is outputted. In the negative peak-hold circuit 14, the negative peak voltage of the AC component S2 is detected and a signal S14 for holding the detected peak voltage is outputted as shown in FIG. 10. In the operational amplifier 15, a differential voltage between the signal S14 and the signal S13 is detected and the detected differential voltage is outputted as an amplitude detect signal S11. According to the amplitude detector 11, the peak-to-peak amplitude of the AC component S2 of the video signal S0 can be correctly detected theoretically.
However, in the amplitude detector 1 shown in FIG. 7, if the duty ratio of the video signal S0 is deviated from 0.5, the amplitude detect signal S1 shown in FIG. 8 does not become a half of the peak-to-peak amplitude of the AC component 2, causing an error in a measured value. Consequently, the attenuated amplitude of the video signal S0 cannot be properly amplified for restoring the original signal.
Theoretically, the amplitude detector 11 shown in FIG. 9 can correctly detect the peak-to-peak amplitude of the AC component S2 of the video signal S0. Actually, however, the characteristic of the positive peak-hold circuit 13 and the characteristic of the negative peak-hold circuit 14 are not exactly in symmetry, so that an error occurs also in the amplitude detect signal S11.
It is therefore an object of the present invention to provide an amplitude detector capable of properly detecting an amplitude of a video signal for example.
In carrying out the invention and according to one aspect thereof, there is provided an amplitude detector comprising: a first peak holding means for generating a first peak voltage signal for holding a peak voltage of a detected signal; a differential signal generating means for generating a differential signal between the first peak voltage signal and the detected signal; and a second peak holding means for generating an amplitude detect signal holding a peak voltage of the differential signal.
In carrying out the invention and according to another aspect thereof, there is an amplitude detector comprising: a first peak holding means for generating a first peak voltage signal for holding a peak voltage of a detected signal; a first differential signal generating means for generating a first differential signal between the first peak voltage signal and the detected signal; a second peak holding means for generating a first amplitude detect signal holding a peak voltage of the first differential signal; a third peak holding means for generating a third peak voltage signal for holding a peak voltage of a reference signal; a second differential signal generating means for generating a second differential signal between the third peak voltage signal and the reference signal; a fourth peak holding means for generating a second amplitude detect signal holding a peak voltage of the second differential signal; and a third differential signal generating means for generating a third amplitude detect signal corresponding to a difference between the first amplitude detect signal and the second amplitude detect signal.
In the amplitude detector according to the invention, if the duty ratio of the input signal varies to vary an DC offset, the waveform of the first peak voltage signal follows the peak value of the input signal. Therefore, in the differential signal generating means, obtaining the difference between the first peak voltage signal and the input signal can obtain the differential signal indicative of the potential of the input signal relative to the first peak voltage signal. In the differential signal, the DC offset is canceled. Therefore, the amplitude detect signal having the peak-hold waveform of the differential signal correctly reflects the amplitude of the input signal relative to the output potential of the amplitude detect signal when the amplitude of the input signal is zero.
In carrying out the invention and according to still another aspect thereof, there is provided an equalizer comprising: a filter means for extracting a high-frequency component from an input signal to provide a first signal; a first amplifying means for amplifying, based on an amplification factor control signal, the first signal to generate a second signal; a second amplifying means for amplifying the input signal to generate a third signal; a superimposing means for superimposing the second signal and the third signal on each other to generate a fourth signal; and an amplitude detecting means for detecting an amplitude of the fourth signal to generate, based on the detected amplitude, the amplification factor control signal; the amplitude detecting means having a first peak holding means for generating a first peak voltage signal for holding a peak voltage of the fourth signal, a first differential signal generating means for generating a first differential signal between the first peak voltage signal and the fourth signal, a second peak holding means for generating a first amplitude detect signal holding a peak voltage of the first differential signal, a third peak holding means for generating a third peak voltage signal for holding a peak voltage of a reference signal, a second differential signal generating means for generating a second differential signal between the third peak voltage signal and the reference signal, a fourth peak holding means for generating a second amplitude detect signal holding a peak voltage of the second differential signal, and a third differential signal generating means for generating the amplification factor control signal corresponding to a difference between the first amplitude detect signal and the second amplitude detect signal.